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. 2010 Dec;19(6):e24.
doi: 10.1136/qshc.2008.031435. Epub 2010 Aug 2.

Impact of sample size on variation of adverse events and preventable adverse events: systematic review on epidemiology and contributing factors

Constanze Lessing  1 , Astrid Schmitz, Bernhard Albers, Matthias Schrappe
Affiliations

Impact of sample size on variation of adverse events and preventable adverse events: systematic review on epidemiology and contributing factors

Constanze Lessing et al. Qual Saf Health Care. 2010 Dec.

Abstract

Objectives: To perform a systematic review of the frequency of (preventable) adverse events (AE/PAE) and to analyse contributing factors, such as sample size, settings, type of events, terminology, methods of collecting data and characteristics of study populations.

Review methods: Search of Medline and Embase from 1995 to 2007. Included were original papers with data on the frequency of AE or PAE, explicit definition of study population and information about methods of assessment. Results were included with percentages of patients having one or more AE/PAE. Extracted data enclosed contributing factors. Data were abstracted and analysed by two researchers independently.

Results: 156 studies in 152 publications met our inclusion criteria. 144/156 studies reported AE, 55 PAE (43 both). Sample sizes ranged from 60 to 8,493,876 patients (median: 1361 patients). The reported results for AE varied from 0.1% to 65.4%, and for PAE from 0.1% to 33.9%. Variation clearly decreased with increasing sample size. Estimates did not differ according to setting, type of event or terminology. In studies with fewer than 1000 patients, chart review prevailed, whereas surveys with more than 100,000 patients were based mainly on administrative data. No effect of patient characteristics was found.

Conclusions: The funnel-shaped distribution of AE and PAE rates with sample size is a probable consequence of variation and can be taken as an indirect indicator of study validity. A contributing factor may be the method of data assessment. Further research is needed to explain the results when analysing data by types of event or terminology.

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Conflict of interest statement

Competing interests: None.

Figures

Figure 1
Figure 1
Flow chart of studies retrieved and included in the systematic review. AE, adverse event; PAE, preventable adverse event.
Figure 2
Figure 2
Adverse event estimates in correlation to sample size (n=144 studies), sample size displayed with half logarithmic-scale.
Figure 3
Figure 3
Preventable adverse event estimates in correlation to sample size (n=55 studies), sample size displayed with half logarithmic-scale.
Figure 4
Figure 4
Adverse event estimates by event type (n=144 studies).
Figure 5
Figure 5
Adverse event estimates by AE terminology (n=144 studies).
Figure 6
Figure 6
Adverse event estimates by types of data collection methods, only single methods are displayed (n=88 studies).
See this image and copyright information in PMC

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Publication types